This invention arose from a search for a better way of steering track-laying vehicles, although the resulting discoveries also apply to many types of wheeled vehicles. Track-laying vehicles, such as tractors, are steered by a clutch and brake system that can unclutch the power to one track and brake one track while another track drives. Such arrangements are expensive and troublesome for many reasons, however.
For example, disconnecting power to the left track of a tractor running on level ground tends to make the tractor turn left because the driving right track outdistances the left, but doing the same thing when the tractor is running downhill tends to make it turn right because the engine holds the right track back while the left rolls free. Braking tracks to slow down tends to straighten the line of travel so drivers must guard against braking on curves. Also, the sharpest turn a track-laying vehicle can make is by braking one track while driving the other, and this stresses the braked track considerably.
In searching for a better solution for these and other problems, we have discovered a way of imposing differential rotation on axle shafts for steer driving both track-laying and wheeled vehicles. Many of these use differential reduction gear drives on opposite sides of the vehicle for turning drive wheels or sprockets, and we have devised an effective way of applying our steer drive system to such reduction gear drives. Our system can simultaneously drive wheels or tracks forward on one side of a vehicle and backward on the other side to allow pivot turns around a central point without overly stressing tracks or wheels. Our system can apply main propulsion drive torque to such pivot turns to accomplish them rapidly, if necessary. Our discovery also provides a steer drive that can avoid slip, even when traction is greatly different on opposite sides of the vehicle, and can apply more power to the side with the greater traction, to get the most from whatever traction is available. Our invention accomplishes these advances by combining inexpensive and well-known components in ways that produce improved results.